UDM broken after removing OX

Hi,

I sunsetted my OX server finally but was not able to remove OX completely. After removing ox-connector and oxseforucs from the OX server and the master.
Now I cannot modify any user objects:

# udm users/user modify --dn uid=testuser,cn=users,dc=mydomain,dc=intra --append mailAlternativeAddress=testmailaddress@mydomain.dom
LDAP Error: Object class violation: attribute 'oxContextIDNum' not allowed.

I also have issues that the OX domain management is in the management console but unusable, but that is not the issue right now.

I even reinstalled oc-connector and oxseforucs on the master, but that did not help.

I still am on UCS 5.0, patch level 9, erratum 1213 due to an installation of Nextcloud Hub which still prevents upgrading to 5.1 or 5.2

Any ideas?

Best regards,

Dirk